Usually when engineers think of rolled screws, they think of something that isn't very precise—with lead errors in the neighborhood of 0.01 inch per linear ft. Not any longer. Engineers at Nook Industries have reportedly come up with a way to thread roll screws with a lead error of just 0.0001 inch per linear ft—accuracy that's on the order of more expensive ground screws. The only limitation of the rolling process, engineers say, is that the outer diameter of the thread dictates the maximum diameter on the screw. Nook engineers say the advancement was "the result of better control of the rolling process." The benefits, says Chief Engineer Rick Christyson, are the cost savings (he estimates about one third the cost of a ground screw) and shorter, more reliable delivery schedules. Typical lead times for ground screws are variable, ranging from weeks to even months, says Christyson. Rather than going to head-to-head with ground screws, though, Nook says that it will target the market served by servo-hydraulics, which involves high loads, high speeds, and precision motion. Though the company won't release the new rolled screws until this summer, it's currently Beta-testing them with several customers in the OEM machine market. So far, so good, says Nook.
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